Thin films play an important part in a wide range in the current society and are utilized in a variety of areas in our daily life such as wrapping papers, magnetic tapes, capacitors, semiconductors or the like. The basic trends of technology including high performance and miniaturization in recent years cannot be discussed without referring to such thin films. At the same time, various methods for forming a thin film have been under development to satisfy industrial demands. For example, continuous winding vacuum evaporation, which is advantageous to highspeed mass production, has been performed to form the thin films for use in wrapping papers, magnetic tapes, capacitors or the like.
In this case, a thin film having desired characteristics can be formed by selecting an evaporation material and a substrate material to meet the purpose of the thin film to be formed and introducing a reactive gas in a vacuum chamber, if necessary, or forming the thin film while applying an electric potential to the substrate.
For example, in the production of a magnetic recording medium, a long magnetic recording medium can be obtained by performing reactive evaporation with an evaporation material containing a magnetic element such as Co, Ni, Fe or the like while introducing an oxygen gas into the vacuum chamber.
Furthermore, for semiconductors, thin films are formed primarily by sputtering. Sputtering is particularly effective in forming thin films with a ceramic based material. A ceramic thin film having a thickness of several .mu.m or more is formed by coating and firing, and a ceramic thin film having a thickness 1 .mu.m or less often is formed by sputtering.
On the other hand, when a resin material is used to form a thin film, a coating method is used. Reverse coating or die coating is used industrially and generally a material diluted with a solvent is applied, dried and cured. Furthermore, the lower limit of the thickness of the resin thin film formed by these methods is often around 1 .mu.m, although it may be varied depending on the material used. It is often difficult to obtain a thickness 1 .mu.m or less. The thickness of coating by a common coating technique is several .mu.m or more immediately after coating. Therefore, the material is required to be diluted with a solvent to form a very thin resin film, and a resin thin film having a thickness of 1 .mu.m or less often cannot be obtained.
Furthermore, the solvent dilution is not preferable, because the dilution with a solvent causes defects readily in a coating film after drying, as well as in view of environmental protection. Therefore, a method for forming a resin thin film without the solvent dilution and a method by which a very thin resin film can be obtained stably are in demand.
As a method to solve this problem, a method for forming a resin thin film in a vacuum has been proposed (e.g., U.S. Pat. No. 5,032,461). In this method, a resin material is atomized in a vacuum and then allowed to adhere to a support. This method permits a resin thin film to be formed without void defects and eliminates the solvent dilution.
The lamination of different thin films on a ceramic thin film or a resin thin film has achieved various complex thin films that had not been realized before and is used in various industrial fields. Above all, in the field of a chip-form electronic component, which is particularly promising, the method of laminating thin films is achieving significantly compact and high-performance capacitors, coils, resistors, capacitive batteries, or complex components thereof, and the commercialization and the market expansion of these components have started already.
In the electronic component formed of thin films, in addition to the basic performance, the connection to the electrode is important. Especially, when a conductive portion is made of a thin film, for example, in a chip component where a ceramic thin film or a resin thin film and a metal thin film are laminated, an auxiliary electrode for soldering may be provided at ends of the thin films to ensure sufficient electrode strength for mounting.
In this case, for adhesive strength between the auxiliary electrode and the metal thin film, it is effective to form a dummy electrode in contact with the auxiliary electrode. For example, when a dielectric thin film made of a ceramic thin film or a resin thin film and a conductive thin film are laminated, the following structure is preferable. As shown in the schematic view of FIG. 6, a dielectric thin film 4 is formed on a first conductive thin film 1a, and a second conductive thin film 1b is formed on the dielectric thin film 4. Furthermore, a third conductive thin film 2a having approximately the same electric potential as that of the second conductive thin film 1b is formed as a dummy electrode approximately in the same surface on which the first conductive thin film 1a is formed with an insulating region 20 therebetween, and a fourth conductive thin film 2b having approximately the same electric potential as that of the first conductive thin film 1a is formed as a dummy electrode approximately in the same surface on which the second conductive thin film 1b is formed with the insulating region 20 therebetween.
Thereafter, when auxiliary electrodes 3 are formed at the ends of the thin films, the auxiliary electrodes are attached not only to the first and second conductive thin films 1a and 1b as the fundamental and normal electrodes, but also to the third and fourth conducive thin films 2a and 2b which are the dummy electrodes, so that the adhesive strength of the auxiliary electrodes 3 can be improved. The smaller dummy electrode portions 2a and 2b are more preferable in view of the miniaturization of the chip component.
However, when the dummy electrodes are used as described above, although the adhesive strength is improved, a problem may arise in the characteristics.
More specifically, it is found that the characteristics of the electronic component are degraded because the dummy electrodes function as electrodes, resulting in a detriment to the achievement of high performance. For example, when a capacitor including the dummy electrodes as shown in section in FIG. 6 is formed, the steepness at the drop point (dip point) in the frequency characteristics of the impedance may become slightly less prominent, and the impedance at the dip point in this case increases by 10 to 15%.
The impedance at the dip point is important for noise removal or filter formation by using a capacitor. Therefore, both of the adhesive strength of the auxiliary electrode and the high performance have been required to be achieved. Furthermore, a similar problem arises in formation of a chip coil having the dummy electrode.